Multiple targets is not the same thing as multiple hits on one target. Those few spells (like Repel Undead) that *do* allow spell power to specifically focus on a single target say so, which implies that only spells that say so have this option. In the case of multiple bolts, I can see the argument, as the spell creates and launches physical fire bolts that could presumably then hit anything. However, by the same logic, I would say that the description of the "Area of Effect" as "1 target" for bolt spells is wrong, as the magic actually affects one bolt, which then may be launched at a target. I could also see taking the +1 target effect and ruling that the bolt hits the primary target, then "leaps" to the secondary target (with a +0 OB - even Triad bolt spells don't let you apply Directed Spells skill multiple times). Depends on how "magical" the GM wants the elements to be. If Fire Bolt launches normal fire by means of magic, that's a bit different from a Fire Bolt of magical fire.
When it comes to multiplying concussion hit damage, that was available in RM2 core (or at least it was a Spell Law option). However, instead of buying a skill up to boost for free, you spent extra PPs. I think the threat of mega-Fire Balls is probably more a balance concern, especially if you let Spell Master stack with Talents and with Spell Enhancement. That could get seriously gross.
